[SPARK-8926][SQL] Code review followup.

I merged https://github.com/apache/spark/pull/7303 so it unblocks another PR. This addresses my own code review comment for that PR.

Author: Reynold Xin <rxin@databricks.com>

Closes #7313 from rxin/adt and squashes the following commits:

7ade82b [Reynold Xin] Fixed unit tests.
f8d5533 [Reynold Xin] [SPARK-8926][SQL] Code review followup.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/ExpectsInputTypes.scala

@@ -39,8 +39,8 @@ trait ExpectsInputTypes { self: Expression =>
   override def checkInputDataTypes(): TypeCheckResult = {
     val mismatches = children.zip(inputTypes).zipWithIndex.collect {
       case ((child, expected), idx) if !expected.acceptsType(child.dataType) =>
-        s"Argument ${idx + 1} is expected to be of type ${expected.simpleString}, " +
-        s"however, ${child.prettyString} is of type ${child.dataType.simpleString}."
+        s"argument ${idx + 1} is expected to be of type ${expected.simpleString}, " +
+        s"however, '${child.prettyString}' is of type ${child.dataType.simpleString}."
     }
 
     if (mismatches.isEmpty) {

sql/catalyst/src/main/scala/org/apache/spark/sql/types/AbstractDataType.scala

@@ -36,12 +36,28 @@ private[sql] abstract class AbstractDataType {
   /**
    * Returns true if this data type is the same type as `other`.  This is different that equality
    * as equality will also consider data type parametrization, such as decimal precision.
+   *
+   * {{{
+   *   // this should return true
+   *   DecimalType.isSameType(DecimalType(10, 2))
+   *
+   *   // this should return false
+   *   NumericType.isSameType(DecimalType(10, 2))
+   * }}}
    */
   private[sql] def isSameType(other: DataType): Boolean
 
   /**
    * Returns true if `other` is an acceptable input type for a function that expectes this,
    * possibly abstract, DataType.
+   *
+   * {{{
+   *   // this should return true
+   *   DecimalType.isSameType(DecimalType(10, 2))
+   *
+   *   // this should return true as well
+   *   NumericType.acceptsType(DecimalType(10, 2))
+   * }}}
    */
   private[sql] def acceptsType(other: DataType): Boolean = isSameType(other)
 

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/AnalysisErrorSuite.scala

@@ -58,7 +58,7 @@ class AnalysisErrorSuite extends SparkFunSuite with BeforeAndAfter {
         }
       }
 
-      errorMessages.foreach(m => assert(error.getMessage.toLowerCase contains m.toLowerCase))
+      errorMessages.foreach(m => assert(error.getMessage.toLowerCase.contains(m.toLowerCase)))
     }
   }
 
@@ -68,21 +68,21 @@ class AnalysisErrorSuite extends SparkFunSuite with BeforeAndAfter {
     "single invalid type, single arg",
     testRelation.select(TestFunction(dateLit :: Nil, IntegerType :: Nil).as('a)),
     "cannot resolve" :: "testfunction" :: "argument 1" :: "expected to be of type int" ::
-    "null is of type date" ::Nil)
+    "'null' is of type date" ::Nil)
 
   errorTest(
     "single invalid type, second arg",
     testRelation.select(
       TestFunction(dateLit :: dateLit :: Nil, DateType :: IntegerType :: Nil).as('a)),
     "cannot resolve" :: "testfunction" :: "argument 2" :: "expected to be of type int" ::
-    "null is of type date" ::Nil)
+    "'null' is of type date" ::Nil)
 
   errorTest(
     "multiple invalid type",
     testRelation.select(
       TestFunction(dateLit :: dateLit :: Nil, IntegerType :: IntegerType :: Nil).as('a)),
     "cannot resolve" :: "testfunction" :: "argument 1" :: "argument 2" ::
-    "expected to be of type int" :: "null is of type date" ::Nil)
+    "expected to be of type int" :: "'null' is of type date" ::Nil)
 
   errorTest(
     "unresolved window function",

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/HiveTypeCoercionSuite.scala

@@ -79,6 +79,7 @@ class HiveTypeCoercionSuite extends PlanTest {
     shouldCast(IntegerType, TypeCollection(DecimalType(10, 2), StringType), DecimalType(10, 2))
 
     shouldCast(StringType, NumericType, DoubleType)
+    shouldCast(StringType, TypeCollection(NumericType, BinaryType), DoubleType)
 
     // NumericType should not be changed when function accepts any of them.
     Seq(ByteType, ShortType, IntegerType, LongType, FloatType, DoubleType,